A problem with the spent catalyst regenerator of a fluid catalytic cracking unit (FCCU) has been thorough and even mixing and distribution of the spent catalyst with the oxygen containing gas or air in the catalyst regenerator for burning off the carbonaceous deposits on the catalyst, as "coke", so that the regenerated catalyst may be reused in the FCCU. The efficiency of the regeneration process is dependent upon a uniform distribution of air through the spent catalyst zone.
Inventors have found greater efficiency results with contacting the catalyst with air just over the center of the air distributor or air ring adjacent to where the air initially leaves the air ring. Here the highest carbon content catalyst is exposed to the richest (highest oxygen content) air. Inventors increased efficiency by guiding the catalyst from the spent catalyst stand pipe down into the catalyst regenerator and over near the center of the regeneration zone for obtaining the most even distribution of the spent catalyst and air. To accomplish this guiding of the spent catalyst down to a position just over the air ring and adjacent the center of the air ring, a curved extention tube has been designed and is utilized by being connected to the lower end of the spent catalyst standpipe where it penetrates the catalyst regenerator wall. To provide even distribution of spent catalyst and air, this extension tube angles down sufficiently to maintain gravity and downward flow of the spent catalyst to exit near the center of the distributor. Air jets spaced along the curved extension tube may insure continual movement and propulsion of the spent catalyst to eject over the air ring.
The prior art, as co-assignee's typical U.S. Pat. No. 4,223,843 merely ejected the spent catalyst from a hole in the wall of the spent catalyst regenerator and aimed it in the general direction of the air ring.